2aPP41. Interaural-delay sensitivity to frequency modulation.

Session: Tuesday Morning, December 3

Time:

Data are presented on experiments that compare binaural sensitivity to
sinusoidal amplitude and frequency modulation (SAM and SFM). Among the stimulus
parameters examined are carrier frequency (3--8 kHz), modulation rate (25--800
Hz), and depth ((beta)=0.1--2). Observers are most sensitive to interaural
delays in SAM tones at rates of about 50 to 300 Hz, while for SFM tones, best
sensitivity occurs at rates of 200 to 400 Hz. Interaural-delay thresholds for
SFM tones are quantitatively predicted from a stochastic AM-envelope model whose
parameters are uniquely determined from data on SAM tones. The model uses
short-term cross-correlation analysis of Hilbert envelopes at the outputs of a
bank of peripheral bandpass filters. The envelopes are subsequently convolved
with the impulse response of a low-pass FIR filter, followed by additive noise,
and a decision device whose output is a position estimate. The expected value
and variance of estimates are stochastically approximated, from which the model
adaptively tracks the 0.707 probability of a correct response (d[sup ']=0.78) on
the observer's forced-choice psychometric function. [Work supported by NIH.]